Physics 20 2012
CONSERVATION OF ENERGY PART 1: PRACTICE PROBLEMS
1. An 80.0 kg box is pushed up a frictionless incline as shown in the diagram. How much work is done on the
box in moving it to the top? (Hint, think energy, not forces.) (5.49 kJ)
2. A 75 g arrow is fired horizontally. The bow string exerts an average force of 65 N on the arrow over a
distance of 0.90 m. With what speed does the arrow leave the bow string? (39 m/s)
3. In the high jump, the kinetic energy of an athlete is transformed into gravitational potential energy. With
what minimum speed must the athlete leave the ground in order to lift his center of mass 2.10 m and cross
the bar with a speed of 0.80 m/s? (6.5 m/s)
4. A 50.0 kg pole vaulter running at 10.0 m/s vaults over the bar. Assuming that the vaulter's horizontal
component of velocity over the bar is 1.00 m/s and disregarding air resistance, how high was the jump?
(5.05 m)
5. If a 4.00 kg board skidding across the floor with an initial speed of 5.50 m/s comes to rest, how much
thermal energy is produced? (60.5 J)
6. A roller coaster is shown in the drawing. Assuming no friction, calculate the speed at points B, C, D,
assuming it has a speed of 1.80 m/s at point A. (24.3 m/s, 10.1 m/s, 18.9 m/s)
7. A water skier lets go of the tow rope upon leaving the end of a jump ramp at a speed of 14.0 m/s. As the
drawing indicates, the skier has a speed of 13.0 m/s at the highest point of the jump. Ignoring air
resistance, determine the skier’s height H above the top of the ramp at the highest point. (1.38 m)
1
Mrs. Connor
Physics 20 2012
8. A roller coaster vehicle with occupants has a mass of 2.9 x 103 kg. It starts at point A with a speed of 14
m/s and slides down the track through a vertical distance of 25 m to B. It then climbs in the direction of
point C which is 36 m above B. An interesting feature of this roller coaster is that due to cost-over-runs and
poor planning, the track ends at point C. The occupant is the chief design engineer of the roller coaster ride.
Estimate the speed of the vehicle at point B; and then determine whether the fellow survives the ride. (26
m/s)
9. A ski jumper starts from rest 50.0 m above the ground on a frictionless track, and flies off the track at a
45.0° angle above the horizontal and at a height of 10.0 m from the ground. Disregard air resistance.
a.
What is the skier's speed when leaving the track? (28.0 m/s)
b.
What is the maximum height attained? (30.0 m above the ground)
10. The speed of a hockey puck (mass = 100.0 g) decreases from 45.00 m/s to 42.68 m/s in coasting 16.00 m across
the ice.
a.
How much thermal energy was produced? (10.17 J)
b.
What frictional force was acting on the puck? (0.6357 N)
11. A car traveling at 50.0 km/h skids a distance of 35 m after its brakes lock. Estimate how far it will skid if its
brakes lock when its initial speed is 100.0 km/h. What happens to the car's kinetic energy as it comes to
rest? (140 m)
12. During an automobile accident investigation, a police officer measured the skid marks left by a car (mass =
1500 kg) to be 65 m long. If the frictional force on the car was 7.66 kN during the skid, was the car going
faster than the 100 km/h speed limit before applying the brakes? (slower)
13. A 45.0 kg box initially at rest slides from the top of a 12.5 m long incline. The incline is 5.0 m high at the
top. If the box reaches the bottom of the incline at a speed of 5.0 m/s, what is the force of friction on the
box along the incline? (1.3 x 102 N)
14. For a conventional coal burning power plant, the
chemical potential energy in the coal is eventually
converted into electricity. Using the diagram below
describe the energy conversions that take place in a
conventional power plant to produce electricity.
2
Mrs. Connor
Physics 20 2012
15. For a nuclear power plant, the nuclear potential energy in the uranium fuel bundles is eventually converted
into electricity. Using the diagram below describe the energy conversions that take place in a nuclear
power plant to produce electricity.
16. For a hydroelectric power plant, the gravitational potential energy of the water in the dam is eventually
converted into electricity. Using the diagram below describe the energy conversions that take place in a
hydroelectric power plant to produce electricity.
3
Mrs. Connor